Process for refining mineral oils



Patented Oct. 8, 1946 UNITED STATES PATENT OFFICE PROCESS FOR REFINENG MINERAL OILS No Drawing.

Original application August 23,

1940, Serial No. 353,956. Divided and this application June 9, 1944, Serial No. 539,590

2 Claims.

This invention relates to solvent dewaxing and solvent extraction of mineral oils and is more particularly concerned with an improved dewaxing and extraction solvent for use in mineral oil refining.

This application is a division of Serial No. 353 956, filed by us August 23, 1940.

The utility of the unsaturated heterocyclic nitrogen bases in the solvent dewaxing and solvent extraction of mineral oils has long been known to the art. The use of pyridine for extract ing hydrocarbon oils from coal and other bituminous materials was disclosed by Baker, Trans. Am. Inst. Min. Engrs, 20, 159 (1900-1901); by Donath, Zeit. Fiir Angewandte Chemie 19, 657-668 (1906); by Bedson, J. Soc. Chem. Ind., 27, 147 to 150; Hofmann and Damm, Brennstoff Chemie, 4, 65 to 73; and others. The use of pyridine in the solvent fractionation of hydrocarbon oils was disclosed by German Patents 319,656 (1918) and 372,208 (1921), and by the French Patent 598,502 (1924). Poole, in Ind. and Eng. Chem. p. 170 to 177 (1931), discussed the solubility of oil and wax in various solvents, including pyridine. Ferris, et al., Ind. and Eng. Chem. p. 753-761 (1931) reported the investigation of a large number of organic compounds, including pyridine, quinoline and alpha picoline, These materials investigated by Ferris evidently contained some water since the temperatures for complete miscibility with 25 API gravity oil of 0.851 viscositygravity constant, were quite high, as 77 F. for pyridine, 58 F. for quinoline, and 86 F. for alpha picoline, whereas anhydrous pyridine and picolines are miscible with such an oil at temperatures slightly below 1 Numerous United States and foreign patents have been issued covering the use of unsaturated heterocyclic nitrogen compounds for the solvent extraction and solvent dewaxing of mineral oils. Careful examination, however, reveals that in all cases these solvents were restricted in their usefulness as dewaxing solvents by a relatively low solubility for the oil component, as well as for the wax component, particularly at the low temperatures suitable for dewaxing mineral oils to the low pour points required for commercial utility. In all cases where solvent dewaxing of high viscosity index oils to low pour points (0 F. and below) was attempted, it was necessary to use solubility enhancers to hold the oil in solution. The use of these solubility enhancers resulted in a large difierential between the dewaxing temperature and the pour point of the dewaxed oil since such materials in themselves have an appreciable solubility for wax even at the dewaxing temperatures.

One object of this invention is to provide a group of new and improved selective solvents for use in lubricating oil refining. I

Another object of this invention is to provide a dewaxing solvent in which oil and wax are miscible at normal atmospheric temperatures and in which the oily constituents are miscible at dewaxing' temperatures.

Another object is to provide a dewaxing solvent in which the wax constituents are relatively insoluble at dewaxing temperatures- Still another object of this invention is to provide a solvent which may be used advantageously with antisolvents for dewaxing and for extraction.

Still other objects and advantages will be apparent from a study of the disclosure which follows.

We have discovered that the saturated or par tially saturated heterocyclic nitrogen bases are miscible with petroleum oils at much lower tem peratures than are the corresponding unsaturated compounds. For example, the pipecolines or saturated picolines, (prepared by hydrogenating the 240 to 500 F. fraction of commercial pyridine. which fraction of commercial pyridine is composed substantially of picolines) are completely miscible with a treated dewaxed Mid-Continent residual lube stock of 90 S. U. V. at 210 F. and V. I., at 35 F., while a mixture of a similarly selected cut of anhydrous picolines and this same Mid-Continent oil separated into two phases upon cooling the mixture to +5 F. These saturated and partly saturated heterocyclic nitrogen bases have complete solubility for oil and wax at elevated temperatures and show marked antisolvent powers for wax at low temperatures, with complete solubility for the oil component, thus making them excellent solvents for use in the solvent dewaxing of mineral oils to produce useful oils of low pour point. The addition of hydrogen to the unsaturated nitrogen compounds has increased their miscibility with hydrocarbon oils at low temperatures. These saturated and partially saturated bases include such compounds as piperidine, pyrroline, pyrrolidine, hydrogenated pyridines, pyrazoline, pyrazolidine, etc., and their alkyl derivatives, as the pipecolines, methyl pyrrolidines, etc.

As an additional advantage, we have found that while the unsaturated bases such as picolines are completely miscible with water the corresponding saturated compounds, the pipecolines,

are not miscible with water in all proportions. For example, the addition of two volumes of water to one volume of anhydrous pipecolines results in the formation of two phases of approximately equal volume. This property makes the drying of these solvents after use in dewaxing or solvent extraction less difiicult.

Commercial pyridines are usually mixtures of pyridine and pyridine homologues and applicants have found that their preferred solvent may be prepared by hydrogenation of that fraction of commercial pyridine, picoline, quinoline, etc., boil- 3 ing between 240 and 500 F, This hydrogenated product consists essentially of hydrogenated picolines, commonly called pipecolines, with some other nitrogen base compounds in smaller proportions. The hydrogenation of this 240-500 F. commercial pyridine fractions lowers the boiling range of the fraction to approximately 215-450 F., since the boiling points of the hydrogenated pyridine, picolines, quinolines, etc., are ordinarily *60 F. lower than the boiling points of the unhydrogenated parent compounds, for example:

Unsaturated heterocyclic Corresponding hydrogenerated nitrogen base, B. P.

nitrogen base, B. P.

Pyridine, 239 F.

Alpha picoline, 264 F. Beta picoline, 290 F. Gamma picoline, 289 F. Quinolinc, 457 F.

Piperidine, 228 F.

3 methyl piperidine, 240 F.

3 methyl piperidiue, 259 F.

4 methyl piperidine, 264 F. Deca-hydro quinoline, 400 F.

10% out No.

Itmight be mentioned that some commercial pyridines contain much higher boiling material than the above given example.

We have found that when desired, the above mentioned saturated and partially saturated heterocyclic nitrogen containing compounds, as the pipecolines, may beused with known wax antisolvents, such as low boiling alcohols, acetone, methyl ethyl ketone and/or other aliphatic or aromatic ketones, aniline, nitrobenzene, pyridine, picolines, pyrrol, etc., to give exceptionally low pour point oils.

It should be added that a blend of pipecoline with furfural or phenol would not be a satisfactory solvent since pipecoline reacts with these two materials to form complex dye-like substances which are not stable to distillation.

'Acetone is recognized as, an ideal antisolvent for wax. Wyant and March, Bureau of Mines, Technical paper 368 (1925), found acetone to be well adapted to the separation of wax from oil .and listed among its advantages:

(1) Oil and wax completely soluble in acetone at (2) At temperatures below 90 F., the separation of wax and solvent is sharp.

(3) The solubility of commercial wax is very low at temperatures of 50 to F.

(4) The wax crystals are large and easily filterable.

(5) Acetone boils at a low temperature, 134 F.,

and it may be completely removed from the oil.

Acetone, however, has a very low solvent power for oil and for this reason, it is not practical to attempt to manufacture lubricating oils of low pour point, such as 0 F. or below, by the use of acetone alone as a dewaxing solvent since the oil-wax-solvent mixture separates into two liquid phases at low temperatures. The oil phase is highly viscous and filtration of wax from this phase is difficult. This disadvantage has been overcome by blending supplementary solvents or solvent enhancers with the acetone to hold the oil in solution. Examples of materials suitable for use as solubility enhancers are: Petroleum naphthas, benzene, toluene, isopropyl ether, etc. Unfortunately, however, these materials have a rather high solubility for wax as well as for oil at the dewaxing temperatures. When the solvent is removed from the oil after the dewaxing operation, this dissolved wax remains in the oil, resulting in an oil of high pour point, or a large differential between dewaxing temperatures and the pour point of the recovered oil. As examples of such blends, the following experiments are cited:

(1) One volume of treated dewaxed Mid-Continent lubricating oil stock of 90 S. U. V., at 210 F. and V. I., was mixed with one volume of a solvent composed of 40% acetone, 40% benzol and 20% toluol. A phase separation occurred on chilling to +10 F.

(2) One volume of treated dewaxed Mid-Continent lubricating oil stock of S. U. V., at 210 F. and 85 V. I., was mixed with one volume of a solvent composed of 30% acetone, 50% benzol and 20% toluol. A phase separation occurred at -15 F.

(3) One volume of treated waxy Mid-Continent residual lubricating oil stock was mixed with four volumes of a solvent composed of 30% acetone, 50% benzene and 20% toluol, chilled to 0 F. and filtered. The recovered oil was of +15 F. pour point, 83 V. I., and 83 S. U. V. at 210 F.

Thus, the maximum proportion of acetone which could be used in the solvent; for dewaxing at 0 F. was about 30%, and under these conditions the solubility of the wax at 0 F. was sufficiently high as to give a +15 F. pour point on the recovered oil. Furthermore, when benzene alone is used as a diluent, it tends to crystallize out of solution at low temperatures. When a third component such as toluol is used to prevent the freezing out of the benzol the resulting three component mixture is difficult to maintain in the proper ratio due to difference in boiling points and water solubility of the three components. When attempts are made to blend acetone with the more selective solvents, such as furfural, nitrobenzene, phenol, chlorex, pyridine, etc., the resulting solution has such a low solvent power for oil at low dewaxing temperatures that dewaxing can be carried out only at high temperatures with the production of high pour point oils.

Our new group of solvents, the saturated and partially saturated heterocyclic nitrogen bases, are excellent antisolvents for wax and have a high solubility for oil at low temperatures. It is therefore possible to blend as much as 40% of acetone or similar antisolvent for wax with these solvents to produce a dewaxing solvent which has complete solubility for high viscosity index oils at to F. For example:

( 1) One volume of treated dewaxed Mid-Continent residual lube stock of 90 S. U. V. at 210 F. and 85 V. I., was mixed with one volume of solvent composed of acetone and 60% pipecolines, prepared by hydrogenating the 240 to 500 F. fraction of commercial pyridine, which fraction of commercial pyridine is composed substantially of picolines. On chilling, a phase separation occurred at -5 F.

(2) One volume of treated waxy Mid-Continent residual lubricating stock, approximately 70 S. U. V. at 210 F. and 90 V. 1., was mixed with three volumes of a solvent composed of 40% acetone and 60% pipecolines prepared as in above Example I. The solution was mixed thoroughly, shock chilled to 0 filtered and the solvent removed by distillation. An oil of 0 F. pour point was obtained.

Thus while it is known to mix as much as l0% acetone with such. auxiliary solvents as naphtha, acetone and benzol, such solvents are limited in use with medium and high V. I. oils to dewaxing temperatures above 0 F. Moreover, the benzol i non-selective, and is diflicult to keep in solution at low temperatures. It has not heretofore been known to blend as high as 40% acetone with selective type solvents for use in dewaxing at 0 F. and below, due to miscibility considerations. With our selectiv solvents comprising large proportions of acetone, it is possible to realize all the advantages of acetone dewaxing without the disadvantage of low solubility for oil, and at the same time the acetone is assisted in its wax precipitating action by the selective solvent which has a relatively high antisolvent power for wax. With these blended solvents, it is possible to produce low pour point oils with practically no differential between the dewaxing temperature and the pour point of the recovered oil. Moreover, the wax crystals formed from our blended solvent are distinct, sharp edged, and filtration is readily accomplished at high rates. Thus, as an additional contribution to the art, our invention discloses a method wherein the utility of acetone in solvent dewaxing is widely extended.

Weir, U. S. Patent 2,154,190, disclosed the use of blends of 40% nitrobenzene with 60% of anhydrous pyridine as a dewaxing solvent. This blend was claimed to have exceptional properties as a dewaxing solvent since the resulting dewaxed oils were stated to be of lower pour point than the dewaxing temperatur He was restricted, however, to dewaxing temperatures of to F., and higher, since at lower temperatures an oil phase separated due to the low solubility of the blend for oil.

Our investigation disclosed the following:

(1) One volume of anhydrous picolines (commercial pyridine, dried and fractionated to 250 to 300 F.) was mixed with one volume of treated dewaxed Mid-Continent residual lubricating oil stock of 90 S. U. V. at 120 F. and 85 V. I. On chilling, an oil phase separated at +6 F.

6 (2) One volume of a solvent composed of 60%? anhydrous picolines mentioned in (1) and 40% nitro benzene, was mixed with one volume of the above dewaxed lubricating oil stock. On cooling, 2. phase separation occurred at 50 F.

(3) One volume of a solvent composed of 60% anhydrous pipecolines (hydrogenated picolines prepared by hydrogenation of the picoline fraction mentioned in (1) above) and 40% nitrobenzene, was mixed with one volume of the above dewaxed lubricating oil stock. On chilling, a phase separation occurred at 0 F.

Thus we are enabled to dewax at temperatures as low as 0 F. using a blend of 40% nitrobenzene with 60% pipecolines (hydrogenated picolines). By so operating, we have greatly extended the utility of nitrobenzene in solvent dewaxing.

This invention is not to be limted in any manner by the heretofore given examples which are for purposes of illustration only. It should be understood that the alkyl derivatives of the above saturated or partly saturated heterocylic nitrogen compounds are closely related in physical and chemical properties and that these derivatives singly or in mixtures which exist in suitable boiling point range, for example, 240 to 500 F., and melting point range suitable for use at dewaxing temperatures, as to permit separation from oil and wax, are satisfactory within degree for use as given.

Mixtures of these materials and similar materials are suitable. Such mixtures may be obtained by hydrogenation of commercial pyridine, picolines, quinolines, selected cuts of nitrogen compounds from coal tar oils, or hydrogenation of the nitrogen bases recovered from petroleum. A convenient method of obtaining useful dewaxing solvents consisting of blends of saturated and partially saturated heterocyclic nitrogen bases in pyridine, picoline, quinoline, etc., is to hydrogenate by conventional methods the said pyridine,

picoline, quinoline, etc., to such an extent as to produce a mixture comprising hydrogenated and partially hydrogenated compounds.

The solvent mixtures and solvent concentrations may be varied and used in many ways as will be understood by those skilled in the art. By increasing the proportions of antisolvent in the mixtures, the resulting solvent may be used advantageously for solvent extraction of mineral oils at convenient temperatures, such as atmospheric temperatures.

An example of the use of our solvent for solvent extraction of a lubricating oil stock is as follows:

A sample of Mid-Continent bright stock was batch extracted at 86 F. with 4 volumes of our blended solvent (25% pipecoline prepared as above disclosed, and acetone). Yields and tests on the stock and resulting products are:

ing markedly improved qualities over those of the original stock was obtained.

A suggested application of solvent extraction and solvent dewaxing of a lube oil stock with a solvent comprising a blend of acetone and pipecoline includes the following steps:

1. Extraction with blended solvent: 75% acetone, 25% pipecoline, prepared as above disclosed.

2. Partial distillation of solvent from the raffinate to remove a portion of the acetone, which step also removes the water from the raffinate solution.

3. Addition of sufficient pipecoline to bring the solvent composition to that desired for dewaxing, say about 40% acetone and 60% pipecoline.

4. Dewaxing of the extracted rafi'inate with said dewaxing solvent blend.

The use of regulated quantities of water in selective solvents, partially or completely miscible with water, for the purpose of regulating the solvent power of the mixture is known. Useful solvents may be obtained by the use of regulated quantities of water in the above listed materials disclosed in our invention.

We do not wish to be limited by the particular examples of dewaxing and extraction solvents, or blends of solvents and antisolvents or solubility enhancers, as given heretofore, since many mate rials and combinations of materials having the above described characteristics and properties may be successfully employed in practicing our invention and yet remain within its intended scope.

We claim:

1. The rocess of solvent extraction of mineral oils including the steps of mixing the oil with a solvent mixture comprising a hydrogenated selected fraction of commercial pyridine, an antisolvent, and water, the selected fraction of commercial pyridine boiling between the approximate limits of 240 and 500 F., and the hydrogenated material consisting essentially of pipecollnes and the antisolvent being acetone, thereby forming a raffinate phase and an extract phase, and separating the rafiinate phase from the extract phase.

2. The process of solvent extraction of mineral oils including the steps of mixing the oil with a solvent mixture comprising pipecoline, an antisolvent, and water,-in which mixture the antisolvent is acetone, thereby forming a raflinate phase and an extract phase, and separating the raflinate phase from the extract phase.

JAMES V. MONTGOMERY. L. BARRETT GOODSON. ROBERT W. HENRY. 

